Does application need to do anything to handle database failover?

I'm trying understand database failover (mainly in SQL Server) and what handling is required from application side to have zero downtime (no failures) to handle DB failover? Assuming that DBAs have done the best set-up for SQL servers (primary and some secondary nodes with replication). Now, if one of the nodes fail (or any node is brought down for scheduled maintenance), 1. What happens to the ongoing queries in SQL server? Do they fail or are they transferred to another node? 2. Does the SQL Server jdbc driver connecting to the database get any failures? Will it retry automatically in such cases? Any insights on these basic questions?